The encyclopaedia of cereal diseases

How to use this encyclopaedia

This publication provides easy reference to the diseases of UK cereals and the pathogens responsible (the causal organisms). The diseases are ordered alphabetically by common name (including variants), from ascochyta leaf scorch to yellow rust. The pathogens responsible are also listed alphabetically at the back of the encyclopaedia (alongside the common names). Both the teleomorph (sexual stage) and anamorph (asexual stage) are listed, when appropriate.

A simple glossary of technical terms can also be found at the end of the encyclopaedia.

For each disease, the pages are structured in a similar way. The common name features at the top of each page. A blue box includes the pathogen responsible and the hosts affected. Where fungal pathogens have both a teleomorph and an anamorph, the teleomorph is listed first, with the anamorph in brackets. There then follows a more detailed description of the disease under the following headings; Hosts, Symptoms, Life cycle, Importance. This is complemented by photographs, as appropriate.

The Chemical Company

Cover image: Scanning EM image of yellow rust pustule (Puccinia striiformis). Copyright© Rothamsted Research Ltd (Centre for Bioimaging). Contents

2 How to use this encyclopaedia 59 Powdery mildew 5 Introduction 63 Ramularia leaf spot 6 Ascochyta leaf scorch (spot) 65 Rhizoctonia stunt 8 Barley yellow dwarf virus 67 Rhynchosporium (leaf scald) (BYDV) 69 Septoria tritici (septoria leaf 10 Black point blotch) 12 Black (stem) rust 71 Sharp eyespot 14 Brown (leaf) rust 73 Snow mould (pink snow mould) 17 Bunt or stinking smut 75 Snow rot (grey or speckled snow mould) 19 Cephalosporium leaf stripe 77 Sooty moulds 21 Covered smut 79 Stripe smut 23 Crown rust 81 Take-all 25 Dwarf bunt 83 Tan spot (DTR) 27 Ergot 85 Yellow (stripe) rust 30 Eyespot 88 Glossary 34 Flag smut 92 Index 36 Foot rot 95 Further information 38 Fusarium (foot rot, seedling blight, ear/head blight) 42 Halo spot 44 Leaf and glume blotch 47 Leaf spot 49 Leaf stripe 51 Loose smut 53 Mosaic viruses 55 Net blotch 57 Omphalina patch

3

Introduction

The need to deliver consistent, high The production of this encyclopaedia yields of high quality grain makes was very much a team effort, bringing control of cereal diseases an together Bill Clark of Broom’s Barn important component of successful Research Centre (now at NIAB), who crop management. Recognition of the wrote the text, with Rosie Bryson and disease, and an understanding of the Lindy Tonguç of BASF and Clare Kelly pathogen(s) responsible, is the first and Graham Jellis from AHDB, who step in successful disease control. editied and formatted it. The This encyclopaedia was produced to publication was funded by BASF and help the grower, adviser and others AHDB Cereals & Oilseeds. We hope involved in cereal production you find it interesting and informative. recognise diseases and learn something about them. Symptoms of both common and less frequently found diseases are illustrated and described, together with an outline of the disease cycle of the pathogen and an indication of the importance of the disease. This encyclopaedia is not intended to be a guide to disease control. Such information is readily available elsewhere, for example the principles of wheat disease management can be found in the Wheat disease management guide and current information on fungicide performance is published annually on the AHDB website.

5 Ascochyta leaf scorch (spot)

Pathogen: Didymella exitialis (Ascochyta spp.)

Wheat Barley Oats Rye Triticale

Hosts Importance The disease affects wheat, barley, The disease is of relatively minor oats, rye, triticale and many grass importance although in individual species. crops it is likely to add to leaf death in the same way as the septoria Symptoms diseases. Disease symptoms are found on Symptoms are often seen later in the lower leaves early in the season and season towards the end of grain on upper leaves later on. The lesions filling when they are unlikely to cause are usually elliptical and although any yield loss. The teleomorph stage chlorotic at first, soon become buff to of the fungus (Didymella exitialis) is brown in colour, often splitting common in Europe and the air-borne longitudinally. Initially lesions have a ascospores of the fungus are dark brown margin with a papery commonly found in late summer in white centre. The fungus often the UK, where they have been invades damaged leaf tissue such as implicat­ed in late summer asthma. that caused by liquid urea or nitrogen. Symptoms become less distinct with time and become very similar to those caused by S.nodorum. Pycnidia within the lesions are generally black, distin­guishing the disease from S. nodorum which tends to have light coloured pycnidia. Life cycle Pycnidia and mycelium within leaf tissue are thought to survive on crop debris, much like the septoria pathogens. Typical ascochyta lesion showing dark margin and black pycnidia

6 Ascochyta leaf scorch (spot)

Typical ascochyta symptoms on wheat leaves

Brown lesions occur Perithecia and on older leaves pycnidia develop Leaves become infected within lesions by rain splash or as air-borne ascospores

Pycnidia (rain splash)

Ascopores

Pycnidiospores are released from pycnidia Perithecia (wind blown)

Overwinters as mycelium and pycnidia in host debris

Ascochyta leaf scorch (spot) life cycle

7 7 Barley yellow dwarf virus (BYDV)

Virus: Barley yellow dwarf virus (BYDV)

Wheat Barley Oats Rye Triticale

Hosts plants. BYDV is most damaging to The disease affects all cereals and plants infected at early growth grasses. Barley and oats are usually stages; plants can be killed by very more severely affected than wheat. early infections. The effects of BYDV may be exacerbated by other stress Symptoms factors such as adverse weather conditions, soil acidity and other The initial symptoms of BYDV pests and diseases. infection are normally seen as indi­vidual plants with bright yellow Life cycle upper leaves scattered through the crop. Later, as infection spreads, BYDV became much more impor­tant larger areas of the crop become and widespread with the increase in infected, appearing as patches of early-drilling of winter cereals. The bright yellow and severely stunted virus exists as several strains and is transmitted by various species of cereal aphid. The bird-cherry aphid (Rhopalosiphum padi) is the principal vector in the south of England. In the north of England and in the Midlands the grain aphid (Sitobion avenae) is usually more important. In the autumn, BYDV can be introduced into cereal crops in two ways: 1. Direct transfer by wingless aphids living on grass or on vol­unteer cereals which survive cul­tivation and move through the soil colonising the following cereal crop. This is much more common in coastal areas of the south west Wheat plants showing yellowing and red where cereals may follow grass tipping of upper leaves and winters can be mild.

8 Barley yellow dwarf virus (BYDV)

2. Indirect transfer by winged aphids migrating into newly emerged crops from grass or vol­unteer cereals elsewhere. BYDV introduced by winged aphids fly­ing into crops is generally much more common and important than BYDV resulting from direct transfer. Importance With the now common practice of sowing winter barley very early, BYDV has increased in importance in many areas of the UK. The fre­quency of very mild winters has also meant that, for many farms, BYDV is now a regular problem. Early infections can kill patches of plants potentially resulting in large yield losses. BYDV infected patch in a wheat field

Affected plants with Individual plants and small yellow and reddish patches affected leaves and stunting Winged aphids spread virus to other plants

Winged aphids

Direct transfer from grass (wingless aphids) Overwinters in grasses and volunteers

BYDV life cycle

9 Black point

Pathogen: Alternaria spp. and Cladosporium spp.

Wheat Barley Oats Rye Triticale

Hosts grain can lead to poor flour and bran The disease can affect all cereal colour, and rejection on the basis of species although wheat and barley discoloured grains. Durum wheat are most commonly affected. The seems to be particularly­ susceptible. same fungi can cause discolouration The disease is commonly reported to of oats. be more severe on larger grains, so high specific weight grain can have a Symptoms higher incidence. This is thought to Symptoms are only visible after be due to the larger grains producing harvest. Affected grain shows a a more open flo­ret, allowing fungal darkening of the outer coat spores greater access to the germ particularly at the embryo end of end of the grain. the grain. Life cycle The disease is associated with a number of airborne fungi including Alternaria spp. and Cladosporium spp. although the evidence for these fungi actually causing the disease­ is still limited and is mainly circumstantial. High humidity or frequent rainfall from the milky ripe to soft dough stage and lodging can often trigger infection by these fungi. Importance The disease has no significant effect on yield but can have serious implications for the quality of milling wheat, barley and oats for processing. The discolouration of the Darkening of grain at the germ end

10 Black point

Conidia infect ears post GS 75

Dark brown discolouration at embryo end of grain Air-borne conidia

Cladosporium

Seed infection can cause Alternaria poor germination

Overwinters on crop debris and vegetation Black point life cycle

11 Black (stem) rust

Pathogen: Puccinia graminis f.sp. tritici

Wheat Barley Oats Rye Triticale

Hosts Life cycle Puccinia graminis f.sp. tritici is The fungus develops teliospores on specific­ to wheat. the wheat plant which produce a secondary spore, the basidiospore. Symptoms This spore infects a completely different host – the barberry Despite its name, the characteristic (Berberis spp.). A further spore stage, symptoms are brown sporulating the aeciospore, is produced on the pustules which occur in stripes on barberry which can spread and leaves and stems. Later in the reinfect the cereal host. This infection sea­son, black elongate pustules gives rise to the uredospore stage con­taining the teliospores develop, which produces the normal mainly on the stems. symptoms on wheat. Outbreaks in Britain are caused by air-borne spores originating in South West Europe and North Africa so infection

Orange/brown pustules on a wheat leaf Orange/brown pustules on wheat stems

12 Black (stem) rust generally occurs when appropriate air movements occur. The optimum temperature is in excess of 20°C so suitable air movements must be associated with high temperatures. Temperatures below 15°C inhibit development of the disease so it rarely occurs under UK conditions. Importance The disease is very rare in the UK but may occur late in the season. Losses due to the disease in the UK are presently very small. Black stem rust on barberry leaves

Aecium produces Long distance spread by aeciospores uredospores from continental Europe

Sexual phase (spread by insects) Uredium

(Berberis spp.) Re-infection of wheat by barberry uredospores Telia and uredia on Wheat Basidiospores wheat stem or leaf

Basidiospores infect barberry stem and leaves Telia on wheat at end of season Overwinters as teliospores on stubble

Black (stem) rust life cycle

13 Brown (leaf) rust

Pathogen: Puccinia triticina (formerly known as Puccinia recondita f. sp. tritici) – Wheat; Puccinia hordei – Barley; Puccinia recondita – Rye, Triticale

Wheat Barley Oats Rye Triticale

Hosts season, diagnosis is much easier as Puccinia triticina is specific to wheat, the brown pustules tend to be other Puccinia spp. and pathotypes scattered at random compared with can affect barley, rye and triticale but the more striped symptoms of yellow do not cross-infect. rust (Puccinia striiformis). Although symptoms are most common on Symptoms leaves, in severe attacks pustules can also occur on the stem and glumes. Symptoms of brown rust infection are Brown rust infection of the glumes often seen in the autumn on early- can result in a reduction in specific sown crops as individual orange to weight. When leaves begin to brown pustules. With early autumn senesce, a ‘green island’ develops infection individual pustules can be around individual pus­tules. Towards confused with yellow rust, being the end of the sea­son dark orange to brown in colour and about teliospores are sometimes produced. 0.5–1.0mm in diameter. Later in the

Brown rust pustules on wheat Brown rust pustules on barley

14 Brown (leaf) rust

Life cycle The fungus over winters primarily on volunteers and early drilled crops. The alternate hosts for P. triticina include species of thalictrum, isopyrum and clematis, although their role in the life cycle in the UK is not thought to be significant. Until recently the disease was rarely important in the spring as temperatures between 15°C and 22°C, accompanied by 100% relative humidity, are needed for sporulation Brown rust pustules on wheat and spore germination. Consequently, brown rust epidemics have normally occurred during mid to late summer in the UK with dry windy days which disperse spores, and cool nights with dew, favouring the build-up of the disease. However, with mild winters, brown rust can often be found at high levels in the spring. With climate change mild winters and warm springs are likely to become more common which could lead to brown rust becoming a much more common problem earlier in the season. Brown rust pustules on rye

15 Brown (leaf) rust

Importance Until recently brown rust was not considered to be a major problem despite early-sown crops generally carrying high levels of brown rust through the winter. However, the occurrence of new virulent strains overcoming varietal resistance in a few key wheat varieties has moved brown rust up the league table of importance. Severe attacks result in a significant loss of green leaf area and hence yield, infection of the ears will also result in loss of grain quality.

Brown rust pustules and teliospores on rye

Pustules of brown uredia Most rapid spread occurs at erupt from the leaf high temperatures late in the releasing uredospores season Late in season black telia form on leaf surface

Teliospores produce basidia and basidiospores. Aecidial stage found on alternate hosts but rare in UK Slow disease development in spring – infection by wind-borne uredospores Overwinters on volunteers

Brown (leaf) rust life cycle

16 Bunt or stinking smut

Pathogen: Tilletia tritici

Wheat Barley Oats Rye Triticale

Hosts Symptoms The disease is specific to wheat. No symptoms can be observed prior to ear emergence. The flag leaves of infected plants show yellow streaks and plants can be stunted, with ‘squat’, dark grey-green ears and slightly gaping glumes. In infected ears the grain is replaced by seed­like ‘bunt balls’ each containing millions of greasy, black, foul­smelling spores. In severe cases, the whole field may smell of rotting fish. In wet weather the ears may appear to be covered in a black ink ­like substance as the spores ooze out of the protective glumes onto the ear and stem. Wheat flag leaf showing typical yellow streak symptoms Life cycle The spores on the seed surface germinate along with the seed. Each produces a short fungal thread terminating in a cluster of elongated cells. These then produce secondary spores which infect the coleoptiles of the young seedlings before the emergence of the first true leaves. Contaminated wheat grain – bunt balls (left) The mycelium grows internally within and healthy grain (right) the shoot, infecting the developing ear. Infected plants develop apparently normally until the ear emerges and the grain sites can be seen to have been replaced by bunt balls.

17 Bunt or stinking smut

In damp soil, spores usually without treatment the disease can germinate and then, in the absence of build up very rapidly. Dry spores can the host plant, die. However, in dry survive for several years. Harvesting seasons, they may survive in the soil or handling equipment contaminated (especially if they are protected within by spores from an infected crop can the glumes of shed ears) from the introduce the pathogen into seed lots harvesting of one crop to the sowing harvested in the following season. of the next. Wind blown spores, The disease is rare in the UK as the particularly from late-har­vested vast majority of seed is treated with a crops, can contaminate neighbouring fungicidal seed treatment. fields which may present bare soil However, the disease is potentially ready for planting the next crop. very damaging and can lead to Importance complete crop loss due to the grain being unsaleable because of As each bunt ball contains discolouration and smell. Cases millions of spores, the capacity for usual­ly arise from sowing untreated contamination of healthy grain in the farm-saved seed although soil­borne same field is enormous. Thus, if seed infections also occur. is continually saved and re-sown

Infection results in stunted plant and bunted ear

Mycelium from germinating teliospores reaches and follows growing point of wheat plant Bunted ear

Intact bunt balls survive in soil overwinter Wheat kernel Germinating wheat replaced by kernel infected by teliospores in teliospores ‘bunt balls’

Bunt balls broken open during harvesting releasing teliospores which overwinter on seed Bunt or stinking smut life cycle

18 Cephalosporium leaf stripe

Pathogen: Hymenella cerealis (Cephalosporium gramineum)

Wheat Barley Oats Rye Triticale

Hosts The fungus survives in crop debris The disease affects wheat, barley, returned to the soil after harvest. oats, rye and triticale. Importance Symptoms The disease is common at very low Affected plants are usually random­ly levels in the UK and does not cause scattered throughout the crop. economic losses Affected tillers have a single distinct bright yellow stripe on each leaf which extends onto the leaf sheath. All leaves on a tiller usually show symptoms but not necessarily all tillers on a plant. The vascular tissue close to the nodes is fre­quently discoloured. Tillers can ripen prematurely and produce white-heads. Life cycle The fungus causing the disease is soil-borne and enters the roots of plants via physical damage. In the UK this disease used to be common in wheat following grass where high levels of wireworm (Agriotes spp.) were found – causing root damage. Soil-borne conidia nor­mally enter roots through damage in the winter months and the fungus grows in the xylem vessels, blocking vascular tissues, particu­larly at the nodes. Close-up of leaf stripe symptoms

19 Cephalosporium leaf stripe

Cephalosporium leaf stripe on wheat

During winter and early Conidia carried by spring, conidia enter xylem lodge and roots from soil through multiply in nodes and damaged areas leaves

Causes leaf stripe symptoms – usually single yellow stripe on each leaf

Infected debris remains after harvest Sporangia produce conidia which enter soil Fungus survives as saprophyte on straw and other crop debris

Cephalosporium leaf stripe life cycle

20 Covered smut

Pathogen: Ustilago hordei – Barley; Ustilago segetum (Ustilago kolleri) – Oats

Wheat Barley Oats Rye Triticale

Hosts seeds. In either case, the spores The species of the pathogen are crop remain dormant on the outside of the specific, mainly occurring on barley seed until it is sown when they and oats. germinate and infect the developing seedling. The fungus then develops Symptoms with the growing point of the plant until it once again colonises the There are no symptoms of the developing ear. dis­ease before ear emergence. At ear emergence the ears seem to be nor­mal except that the grains appear to be covered in a thin membrane. If this is broken open it can be seen that the grains have been replaced by masses of black spores held in place by the transparent mem­brane. The membrane is relatively easily ruptured and as spores are released the symptoms become sim­ilar to those of loose smut. Life cycle After ear emergence some spores may be released on to the rest of the crop and carried by the wind to neighbouring plants (as in loose smut, caused by U. avenae and U. nuda). However, many are retained within their membranous envelope until the crop is harvested when, during the threshing process, they are released Covered smut affected barley ears (healthy to contaminate the surrounding one on right)

21 Covered smut

Importance The disease is very rare in the UK and is usually only found in crops grown repeatedly from home-saved, untreated seed.

Covered smut on oats

Mycelium invades the grain sites Grain sites replaced by masses of teliospores Mycelium follows growing point of oat plant

Teliospores land on flowers of Healthy grains healthy plants and infect contaminated developing grain with spores

Mycelium invades young seedlings

Mycelium invades embryo in seed

Covered smut life cycle

22 Crown rust

Pathogen: Puccinia coronata

Wheat Barley Oats Rye Triticale

Hosts The basidiospores of this fungus The crown rust fungus affects only infect the alternate hosts, the oats: it does not attack other cere­als. buckthorn (Rhamnus catharticus) and It can infect a number of grass­es, alder buckthorn (Frangula alnus) on particularly ryegrass but the forms on which are produced a third spore grass do not cross infect to oats. type, the aeciospores, which can then infect oats once again. Symptoms The first symptoms of crown rust are very similar to brown rust of wheat and barley. Orange-brown pustules appear scattered over the leaf surface. Leaf sheaths, and later the oat panicle, can also become infected. The disease is favoured by high temperatures (20–25°C) so epi­demics usually occur in June–July. Late in the season black pustules appear within the existing crown rust lesions. Life cycle The orange spores (uredospores) produced on leaves are air-borne and spread the disease long distances to other plants and adjacent crops. Later in the season black pustules containing teliospores are produced. These remain dormant on crop debris until the spring when they germinate­ to produce basidiospores. Crown rust pustules

23 Crown rust

Uredospores produced in the oat crop also infect volunteer oat plants and then emerging winter oats. Importance The disease is favoured by warm and humid weather and mild winters. Severe attacks have been more common in recent years. Such epidemics can reduce yield by 10–20%.

Buckthorn leaf showing aecidial stage

Uredia develop on oat leaves Oats

Uredium Aecium Buckthorn produces aeciospores

Overwinters on volunteers and Re-infection of winter oats oats by uredospores Basidiospores Basidiospores infect buckthorn and alder Distinctive buckthorn teliospores (alternate hosts) Telia on oats at end of season Overwinters as teliospores on stubble Crown rust life cycle

24 Dwarf bunt

Pathogen: Tilletia controversa

Wheat Barley Oats Rye Triticale

Hosts The disease affects wheat, winter barley, rye and triticale. Symptoms This disease is not yet known in the UK but is of interest because of evidence­ of the long-term survival of bunt (T. tritici) in soil. As dwarf bunt can also survive for long peri­ods in the soil, the possibility of hybrids between T. controversa and T. tritici has been widely debated. Dwarf bunt occurs in Canada, North and South America and many parts of Europe and Asia. Microscopic examination of teliospore morphology is the pri­mary means of distinguishing species of Tilletia. However, there is a wide range of teliospore charac­teristics in Tilletia spp. so spore morphology alone is not a suitable method of identification. The symptoms of dwarf bunt are very similar to bunt except that affected plants are stunted to between half and quarter of their normal height. Infected ears tend to have a more ragged appearance than with bunt. Yellowing and flecking of leaves of affected plants is also Infected ears with slightly 'ragged' occasionally found. appearance

25 Dwarf bunt

Life cycle spores will germinate. As a result, the The disease cycle of T. controversa fungus frequently infects plants much matches that of T. tritici very close­ly. later in development. Infected plants appear unaffected­ At harvest, 'bunt balls' contami­nate until ear emergence. When the ears the soil as well as healthy seed but emerge the seeds are seen to have with dwarf bunt this is very significant been replaced by 'bunt balls' which as the fungus can survive in soil for break open during harvest, many years. Free spores are reported contaminating healthy grain. When to remain viable in soil for at least contaminated grain is sown the three years and 'bunt balls' can fol­lowing season the spores on the survive for up to 10 years. outside of the grain germinate, eventually reaching the growing point Importance of the plant. It is at this stage that Presently, the disease is not known in T. controversa differs from T. tritici. the UK. However, like bunt, the With bunt, the fungus normally infects disease could be very damaging the plant via the coleoptile as the although seed treatments common­ly seedling is emerg­ing. However, with used in the UK would prevent T. controversa, there is a long seed-borne infection. incubation period and a requirement for cool temperatures before the

Infection results in stunted plant and bunted ear

Mycelium from germinating teliospores reaches and follows growing point of wheat plant

Bunted ear

Germinating wheat Wheat kernel kernel infected by replaced by teliospores teliospores in ‘bunt balls’ Bunt balls broken open during harvesting releasing teliospores which overwinter on seed and soil Dwarf bunt life cycle

26 Ergot

Pathogen: Claviceps purpurea

Wheat Barley Oats Rye Triticale

Hosts Life cycle The disease affects all cereal crops Ergot is not truly a seed-borne and a wide range of grasses, dis­ease as it is not carried on or in particularly black-grass (Alopercurus seed. However, it can be spread by myosuroides). ergots in contaminated seed. It is also one of only two diseases which are Symptoms included in the UK Seed Certification The causal fungus only attacks the Scheme for Cereals (the other being ear at flowering, replacing the grain in loose smut). a few spikelets by a hard, purple­black At or near to harvest, ergots fall to the sclerotium, known as an ergot. Such ground where they remain until the ergots can be very large, up to 2cm in following summer, when they length, and are very obvious in the germinate to produce club-shaped standing crop and in contaminated spore-bearing structures (stroma). grain samples. These ascospores are spread by the wind to nearby open flowers of grasses and cereals. The spores ger­minate in the flower, infecting the ovaries. This infection leads to the production of secondary spores (conidia) encased in a sticky secre­tion commonly referred to as hon­eydew. This attracts insects which carry the spores to other flowers where further infection can occur. There are a number of strains of the fungus, some of which can infect grasses and cereals, others which are restricted to certain hosts. Wheat and other cereals are less

Black-grass heads infected with ergot

27 Ergot severely affected than rye although occasionally more open-flowered wheat varieties can be badly affected.­ The disease is favoured by cool, wet conditions during flowering which facilitate spore production and prolong the flowering period­, making infection more likely. Importance The disease has very little direct effect on yield but the ergots con­tain large amounts of toxic alka­loids. Consequently, if grain con­taminated with ergots is fed to stock or used to make flour then there are risks to animal and human health. As a result, contam­inated grain may be rejected. Ergots in a sample of treated seed

Ergots in infected wheat ears Club-shaped, spore bearing structures (stroma) from germinated ergots

28 Ergot

Perithecia release ascospores which infect flowering plant. Mycelium penetrates ovary tissue

Perithecium Ascospores Grains infect grasses – replaced by especially sclerotia black-grass Germinating sclerotia produce stroma containing perithecia Secondary spread from grasses in honeydew Sclerotia overwinter in soil Ergot life cycle

29 Eyespot

Pathogen: Oculimacula yallundae, (Helgardia herpotrichoides) O. acuformis (H. acuformis)

Wheat Barley Oats Rye Triticale

Hosts O. yallundae (W-type) is more pathogenic on wheat and barley than on rye, O. acuformis (R-type) is pathogenic on wheat, barley, rye and triticale. Symptoms Early symptoms can be confused with sharp eyespot and Fusarium spp. Frequently, all that is visible is a brown smudge on the leaf sheath at the stem-base. In early-sown crops eyespot lesions may penetrate one or two leaf sheaths, making identification more conclusive. Lesions caused by Fusarium spp. and sharp eyespot are generally confined to the outer leaf sheath. Later in the season eyespot symp­toms become more distinct and appear as an eye-shaped lesion with a dark margin, usually below the first node. Later still, the margin of the eyespot lesion is often dark and diffuse with a central black ‘pupil’ occasionally visible. In severe attacks of eyespot, white-heads ('bleached' ears) are commonly seen scattered through the crop, later in the season these may become colonised by sooty moulds. White-head symptom in wheat crop

30 Eyespot

Eyespot tends to be more severe if plants are also suffering from take-all. Life cycle The fungus over-winters on infected stubble, volunteers and grass weeds acting as sources of inoculum. It can survive on stubble for up to three years, so a break from cereals will not necessarily reduce eyespot risk in following crops. Spores are produced throughout autumn and winter, posing a threat to early sown crops. Infection occurs at temperatures above 5°C and during wet periods. Spores are rain splashed short distances from infected stubble. The development of symptoms following infection takes 6–8 weeks, depending upon environmental conditions. Eyespot can be a serious problem in contin­uous cereals, where inoculum may build up from year to year. Close-up of eyespot lesions at the stem base The sexual stage of both eyespot fungi may play an important part in the pathogen life cycle. This stage of the fungus is produced on stubble at the end of the season and after harvest, ascospores may travel long distances and infect emerging or young plants.

31 Eyespot

Importance Eyespot is often underestimated in importance because few farmers ever look at the stem bases of crops at the milky ripe stage or later when severe eyespot can often be seen. Moderate or severe eyespot infections can cause yield loss in the order of 10–30%, even in the absence of lodging. Where eyespot is severe, lodging can occur – causing­ problems in harvesting and fre­quently a reduction in Hagberg Falling Number.

Severe eyespot lesions on wheat

Close-up of eyespot lesion on winter wheat

32 Eyespot

Lesions cause white-heads and sometimes lodging ‘Eyespot’ lesions Conidia splash from debris to on stem base young plants. Ascospore infection of autumn sown crops

Sexual stage on straw debris may result in long distance spread of ascospores Eyespot life cycle

33 Flag smut

Pathogen: Urocystis agropyri

Wheat Barley Oats Rye Triticale

Hosts ger­minate, producing a secondary The disease affects wheat and many spore type – the sporidia. These grass species; the strain(s) that affect spores infect the germinating wheat wheat are specific to that crop. seedlings coleoptile. The fungus, having penetrated the seedling, then Symptoms grows inside the plant, eventually­ producing the typical striping on the Affected plants are severely stunt­ed. upper leaves late in the sea­son, Excessive tillering is common and giving rise to a new generation of often the ears fail to emerge, teliospores. The teliospores can remaining within the boot. Plants survive in soil for several years, so show long dark grey to black streaks even where a break from cereals on the leaf blades and leaf sheaths. occurs, subsequent wheat crops may The streaks eventually erupt, giving become infected. the leaves a ragged appearance and exposing the black teliospores which Importance are then dis­persed, giving the plants the appearance of being covered in Flag smut of wheat occurs in some soot. European countries and in Australia, Canada and the USA. However, it was Life cycle not known in the UK until 1998 when an outbreak was confirmed in Essex. The teliospores released from the The dis­ease is not particularly leaves can either be blown onto grain damaging unless present at high of healthy plants, contami­nating the levels but it can have serious grain, or they can drop to the soil consequences with regard to where they are very per­sistent, exporting grain or wheat products. surviving up to four years. When Many countries have quarantine contaminated grain is sown, or if restrictions which pro­hibit the import healthy grain is sown into of wheat products from countries contaminated soil, the teliospores where the disease is established.

34 Flag smut

Streak symptoms of flag smut on a wheat Black teliospores on a wheat leaf leaf Sori develop between veins on leaves and glumes Fungus grows systemically within plant

Sori erupt In autumn and spring sporidia releasing germinate. Mycelium infects spore balls seedlings containing teliospores germinating teliospore spore balls Teliospores germinate forming promycelium and sporidia Overwinters as spore balls on seed in the soil Flag smut life cycle

35 Foot rot

Pathogen: Cochliobolus sativus (Drechslera sorokiniana)

Wheat Barley Oats Rye Triticale

Hosts Importance The disease affects all cereals. Foot rot due to C. sativus is traditionally a disease of hotter Symptoms climates than that of the UK. The fungus causes disease symptoms similar to Fusarium spp. Seed­borne infection can result in seedling death although infected plants usually grow to maturity. Affected plants show brown spot­ting on the lower leaves and, if severely affected, can show stem-base rotting and poorly filled ears. This severe symptom is very rare in the UK. Life cycle The fungus behaves very much like Fusarium spp. in its survival and life history. It is both soil and seed-borne. It infects seedlings as they emerge, occasionally producing a seedling blight. More usually it infects roots of seedlings, allowing the plant to survive. Leaf spotting and stem-base infections produce splash-borne Foot rot discolouration of wheat sub crown spores which can be carried to internode emerging ears resulting in seed infection.

36 Foot rot

Foot rot browning at the base of young barley plants

Diseased plants appear stunted, mature early and have shrivelled grain

Pseudothecia occur on the stem-base at the end of the season

In autumn and spring ascospores and conidia from conidiophores infect roots and stem bases

Overwinters on crop debris as pseudothecia and mycelium Foot rot life cycle

37 Fusarium (foot rot, seedling blight, ear/head blight)

Pathogen: Fusarium spp. and Microdochium nivale

Wheat Barley Oats Rye Triticale

Hosts Wheat, barley, oats, rye, triticale and grasses. Symptoms There are many species of Fusarium that affect cereals. These fungi form a complex of diseases on seeds, seedlings and adult plants. The seed-borne pathogen Microdochium nivale (formerly known as Fusarium nivale) is also usually included in this group of fungi. M. nivale is the primary pathogen in the group which causes seedling Fusarium on the stem-base blight resulting in seedling death and thinning of the plant stand. Other species cause a range of symptoms including brown lesions on stem bases, often restricted to the outer leaf sheath. Fusarium lesions often begin in the leaf sheath at the stem base where crown roots split the leaf sheath when emerging. This infection can then spread up the leaf sheath causing­ long dark brown streaks at the stem base. The most commonly seen symptom in the UK is the dark brown staining of the lower nodes.

Fusarium staining on the lower nodes

38 Fusarium (foot rot, seedling blight, ear/head blight)

Ear blight infection resulting in bleached ears Pink grains caused by Fusarium

On older plants Fusarium infection infected during the early flowering can produce a true foot rot, where the stages. Later infections may result in stem base becomes brown and infection­ of the grain but without rotten, resulting in lodging and obvious bleaching of the ears. The white-heads. ear blight phase of the disease can cause yield loss but is most important This symptom is less common in the as it can result in mycotoxin UK, although it can be found in very production in the grain. Mycotoxins dry seasons. are substances toxic to animals and Many of the Fusarium species cause humans. Levels in grain, flour and a range of symptoms – often termed flour products for human and animal ear blights. F. culmorum and consumption are limited under EU F. gramin­earum are the two most legislation. See Guidelines to commonly found species in the UK. minimise risk of fusar­ium Other species include F. avenaceum, mycotoxins in cereals (AHDB F. poae and F. langsethiae. Infection Cereals & Oilseeds) for more details. frequent­ly results in the whole or part of the ear becoming bleached. This symp­tom is seen when ears become

39 Fusarium (foot rot, seedling blight, ear/head blight)

Ear blight symptoms on wheat (Fusarium poae)

40 Fusarium (foot rot, seedling blight, ear/head blight)

Life cycle Importance The most important source of Symptoms of Fusarium infection are Fusarium on wheat crops is the seed common in wheat crops in the UK but the fungus can also survive on and most cereal crops will have some debris in the soil. In seasons where symptoms of one or other of these weather conditions are wet during diseases. When weather conditions­ flowering and grain formation, spores are wet during flowering, high levels are splashed from lower in the of ear blight can occur but their canopy causing ear blights and incidence is frequently over-estimated seed-borne infection. In such and losses are only rarely serious. seasons seed-borne infection can Severe foot rotting is very rare in the pose a serious threat to crop UK and losses are generally very establishment unless seed is treated small. The seed­borne phase of the to control Fusarium. All of the cereal disease is potentially­ very damaging. Fusarium species are common in soil. Seed treat­ment plays a major role in Most have competitive saprophytic prevent­ing seedling losses in wheat. abilities which allow them to colonise Seedling blight is rare in barley. debris and stubble in soil. Volunteers may also act as a source of inoculum.

Splash dispersal of conidia up plant

Ear blight symptons Dark brown lesions on stem base and vertical streaks up stem

Seed infection

Overwinters on crop debris, grass weeds, volunteers and chlamydospores in soil Seed infection causes damping off and early infection of plant

Fusarium (foot rot, seedling blight, ear/head) life cycle

41 Halo spot

Pathogen: Selenophoma donacis

Wheat Barley Oats Rye Triticale

Hosts Life cycle The disease only affects barley. The disease originates from infect­ed seed, stubble and volunteer barley­ Symptoms plants. Symptoms on lower leaves Halo spot is found mainly in western­ which arise from seed infec­tion or coastal areas where outbreaks occur from stubble contact or splash are in wet summers after flag leaf indistinct but spread up the plant in emergence. The disease appears as rain-splash, usually in warm small leaf spots (1–3mm long) often conditions later in the sea­son. The square or rectangular in shape, pale disease rarely becomes important brown in the centre with dark pur­ple/ until after flag leaf emer­gence when it brown well defined margins. Pycnidia can develop rapidly in wet weather. occur in lines along the veins within the central area of a lesion. Spots Importance generally occur towards the tips and The disease occurs sporadically, along the edges of leaves. They also usually in wet seasons. Traditionally affect the leaf sheath and ear the disease occurs mainly in the (especially the awns). This disease south west of England where rain­fall often occurs with rhynchosporium is high but is rare elsewhere in the but can be distinguished from the UK – it generally does not cause latter by the smaller size of the spots significant yield loss. and the presence of pycnidia within the lesions. Also, halo spot tends to occur most frequently on the upper leaves whilst rhynchosporium­ is often more common on the older foliage.

42 Halo spot

Halo spot symptoms on a barley leaf

Splash dispersal of conidia up plant

Halo spot symptons occur on leaf tissue In autumn and spring crops are infected by pycnidiospores

Pycnidia form in lesions

Overwinters as pycnidia on crop debris Halo spot life cycle

43 Leaf and glume blotch

Pathogen: Phaeosphaeria nodorum (Stagonospora nodorum formerly Septoria nodorum)

Wheat Barley Oats Rye Triticale

Hosts Mainly wheat, but occasionally barley and rye. Symptoms S. nodorum can be seed-borne and infect seedlings, resulting in water­ soaked, dark green areas on the coleoptile, later becoming necrotic. Twisted, distorted and stunted seedlings may also occur. On mature leaf tissue the first symp­toms of infection are small necrotic lesions. Later these develop into brown oval lesions surrounded by a chlorotic halo. These lesions fre­quently coalesce to produce large areas of dead, dry and sometimes split tissue. Pycnidia form within infected tissue, but these are a pale pinkish brown colour and difficult to see in the field, even with a hand lens. They are best seen by viewing the lesions in transmitted light with a hand lens. S. nodorum can also infect the ears, particularly of wheat, causing glume blotch. Dark brown patches like burn-marks develop on the glumes, which later become purple-brown. Glume blotch symptoms are easiest to see on green ears. Glume blotch symptoms on a wheat ear

44 Leaf and glume blotch

Although more usually associated While trash-borne inoculum is usually with necrotic blotching of leaves and more important in initiating the later glumes, S. nodorum can cause phases of the disease (leaf and glume post-emergence seedling blight in blotch), fungus carried on the seed is cool wet soils. more likely to be respon­sible for septoria seedling blight. Life cycle S. nodorum survives as dormant Importance mycelium, and as pycnidia and S. nodorum was once the most pseudothecia on seed, stubble, serious pathogen on cereals in the debris, autumn-sown crops and UK, although it now rarely causes volunteers. In the absence of crop significant losses except in wet debris, initial infections in the autumn seasons in the south west of or spring may result from wind-borne England. Yield losses up to 50% have ascospores released from been reported in trials although pseudothecia long distances away. average annual losses in the UK As temperatures rise and humidity probably do not exceed 3%. Losses increases pycnidiospores are caused by septoria seedling blight produced from the pycnidia. These are generally not significant. are splash-dispersed up the infected plant and from plant to plant. Temperatures of 20–27°C, together with 100% relative humidity, are optimal for spore production and germination and a period of rain is essential for spore dispersal. The disease cycle can be completed in 10–14 days during such conditions. Spores produced from pseudothecia and pycnidia, which develop on the flag leaf and ear at the end of the season, can ini­tiate infection in early autumn-sown crops and volunteers and may also remain dormant for the winter. Glume blotch infection of the ear can lead to infection of the seed. Like the Fusarium spp., S. nodorum can survive between crops either on seed or on plant debris. Glume blotch lesions on wheat leaves

45 Leaf and glume blotch

Leaves and ear infected by contact and rain splash

In spring, crops also infected by pycnospores and ascospores

Pycnospores Ascospores

Seed infection

Overwinters on crop debris, grass weeds, and volunteers Seed infection causes damping off and early infection of plant

Leaf and glume blotch life cycle

46 Leaf spot

Pathogen: Pyrenophora avenae (Drechslera avenae)

Wheat Barley Oats Rye Triticale

Hosts Life cycle The disease is specific to oats. The primary phase of the disease arises from seed-borne infection. Symptoms Spores from the early leaf stripes The primary phase of the disease then splash up the plant, producing (from seed-borne infection) appears the secondary leaf spot phase of the as short brown stripes with purple disease. Eventually spores splash up edges on the emerging leaves. These onto the ear where the grain stripes appear on the first three or becomes infected. Infected grain can four leaves of emerging seedlings. cause seedling death during or soon The secondary phase of the disease after emergence. Surviving seedlings (splash-borne spores) appears as give rise to the primary phase of the red-brown spots with purple mar­gins disease. Infected debris is not on leaves. thought to be a significant part of the disease cycle. Importance The disease is no longer a serious pathogen of oats. Although it is not uncommon, severe outbreaks are very rare and probably associated with repeated home-saving of un­treated seed.

Leaf spot symptoms on oat leaves

47 Leaf spot

Close-up of symptoms showing short brown stripes with purple edges

Conidia are blown onto adjacent ears infecting seeds Conidia are produced on Upper leaves infected leaves with spotting symptons Perithecia may occur but Spread to upper are rare in nature leaves Emerging leaves Seedling Seedling striped infection

Leaf spot life cycle

48 Leaf stripe

Pathogen: Pyrenophora graminea (Drechslera graminea)

Wheat Barley Oats Rye Triticale

Hosts Life cycle The disease is specific to barley. The fungus is present on the seed surface and as mycelium in the seed Symptoms coat. As the coleoptile emerges, the The disease is seed-borne and fungus invades the tissue and caus­es long brown stripes on the pene­trates through to the emerging leaves. The stripes are often pale first leaf. The fungus grows through green at first, becoming yellow and successive leaf sheaths, producing then finally dark brown. Usually all of the characteristic symptoms on each the leaves of affected plants show leaf until it infects the ear which often these symptoms and some leaves remains in the leaf sheath. Although split along the stripes giving the leaf a the fungus pro­duces spores on the shredded appearance. Symptoms are stripes these are not thought to be usually most prominent at ear very important in the UK as a means emergence. The disease is generally of spreading the disease. most severe on crops which have been grown from untreated seed. Importance This is potentially the most serious Leaf stripe can affect the plant in seed-borne disease of barley. If seed three ways; first it can kill seedlings from affected crops is re-sown as they emerge. This is unusual but without an effective fungicidal seed can occur if soil conditions are very treatment being applied, the disease poor. Secondly, it can reduce the can multiply very significantly and efficiency of the plant by reducing produce large yield losses. If seed is green leaf area and thirdly, it can saved and re-sown repeatedly, result in complete blindness of the com­plete crop loss is possible within ear resulting in no harvestable grain a few generations of seed from affected tillers. multiplication.

49 Leaf stripe

Leaf stripe symptoms on barley

Conidia are blown At ear emergence onto adjacent ears conidia are produced infecting seeds on infected leaves

Perithecia may occur but are rare in nature

All leaves show leaf stripe

Overwinters as seed Seedling borne mycelium infection

Leaf stripe life cycle

50 Loose smut

Ustilago nuda f.sp. tritici (U. tritici) – Wheat; Ustilago nuda f.sp. hordei – Barley; Ustilago avenae – Oats

Wheat Barley Oats Rye Triticale

Hosts Symptoms There are distinct forms of the Loose smut is easily recognised at pathogen which are crop specific. ear emergence as individual grains are completely replaced by a mass of black fungal spores. Partly affected ears are sometimes seen. The spores are released as soon as the ear emerges, leaving only the bare remains of the ear rachis. Because the blackened ears are so obvious in the crop at ear emer­gence the disease appears to be very severe, even at very low incidence. Life cycle Spores are released from infected ears and are carried by the wind to the open flowers of surrounding healthy plants. There they germi­nate and the fungus grows into the developing grain site. Weather conditions during flowering affect the length of time that the florets remain open and hence the time that the plant is susceptible to infection. Thus, the likely level of infection varies considerably from season to season. The fungus lies dormant within the embryo of the seed until the seeds Close-up of infected wheat ears are sown and germinate.

51 Loose smut

When the infected seed germinates the fungus grows within the developing shoot, eventually reaching the ear primordia. The fungus develops within the young ear, eventually replacing spikelets with masses of fungal spores which are released once again as the ear emerges. Importance The UK Seed Certification Scheme is undoubtedly successful in ensur­ing that loose smut remains at very low levels in UK seed stocks and is of low importance. Seed crops grown under the scheme are in­spected for loose smut and because the disease is so easily seen at low levels it can be detected by visual examination. Loose smut infected wheat ears

Grain sites replaced by masses of teliospores

Mycelium invades Mycelium follows growing the grain sites point of wheat plant

Teliospores land on flowers of healthy plants and infect developing grain

Mycelium invades young seedlings

Mycelium invades part of embryo in seed Loose smut life cycle

52 Mosaic viruses

Viruses: See below

Wheat Barley Oats Rye Triticale

Mosaic Viruses which are most pronounced during • Barley Yellow Mosaic Virus the early spring, particularly following (BaYMV) a prolonged cold spell. Barley Mild Mosaic Virus (BaMMV) The yellow streaks may become • brown or purple at the leaf tip and • Oat Mosaic Virus (OMV) dark brown flecking may replace the • Oat Golden Stripe Virus (OGSV) yellow streaking. • Soil-borne Cereal Mosaic Virus (SBCMV) • Soil-borne Wheat Mosaic Virus (SBWMV) Each of these mosaic diseases is caused by a virus, transmitted by the soil-borne vector Polymyxa gramin­is. The viruses causing these diseases are closely related single stranded RNA (ribonucleic acid) rod or filamentous viruses belonging to the genus Furovirus or Bymovirus. Hosts The diseases affect only winter-sown crops. All cereals are affected by their own form of the virus which does not cross-infect to other cereals. Symptoms Affected plants can be very stunted Typical yellow streaks and brown flecking of barley yellow mosaic and pale in colour. Typical symp­toms are pale yellow streaks in the leaves

53 Mosaic viruses

Life cycle BaMMV are very common in the UK. The disease often occurs in distinct SBWMV and SBCMV are present in patches which increase in size from the UK but are not yet common­ly one year to the next. The virus is found. OMV is commonly found carried in the soil by the root-infecting OGSV is usually found in association­ organism Polymyxa graminis. with OMV. Movement of the soil during cultivations will spread the disease within the field and to other areas. The virus survives within the spores of the vector so that once it is present in soil it persists even in the absence of cereal crops for many (more than 25) years. Importance Yield losses of 50% have been recorded in the patches on susceptible varieties. BaYMV and Close-up of yellow streak symptoms on oats

Virus particles multiply causing leaf chlorosis and stunting

Polymyxa graminis forms intercellular plasmodia and resting spores

Polymyxa resting spores in root tissue

Polymyxa graminis zoospores carrying virus particles, infect The vector, Polymyxa root hairs graminis overwinters in soil

Mosaic life cycle

54 Net blotch

Pathogen: Pyrenophora teres f. teres (Drechslera teres) Pyrenophora teres f. maculata (spot form)

Wheat Barley Oats Rye Triticale

Hosts Life cycle The disease affects a wide range of Seed-borne mycelium infects the grasses but the forms on barley are coleoptile and the first leaf becomes specific to that crop and do not affect infected as it emerges. Spores other cereals or grasses. pro­duced on this first leaf serve to spread the disease to other leaves Symptoms and to surrounding plants. Infection of young seedlings with net Seed-borne inoculum is usually much blotch can look very similar to leaf less important than infected stubble stripe infection – the first leaf often and debris which allows the pathogen has a single brown stripe extending to over-winter. the whole length of the leaf. However, later leaves do not usually show striped symptoms. Leaves infected by splash-borne spores typically show short brown stripes or blotches with a network of darker lines at random on the leaves. The disease tends to produce ‘stripe’ symptoms or ‘net­ting’ symptoms which are distinctly different in appearance. There is also another, less common symp­tom which is termed ‘spot blotch’ where lesions are more oval in appearance. Leaves frequently have yellowing associated with all of these types of lesion, particularly when the symptoms are severe. The glumes and awns can also be affected,­ producing dark brown flecking and striping. Close-up of typical symptoms of net blotch

55 Net blotch

Trash and crop debris provides much symptoms continue to develop higher levels of inoculum which is through the winter and into the early splash borne up the plant. Although spring, producing an early epi­demic there are suggestions of long as the crop develops. distance spread of ascospores from over­wintering pseudothecia the role of these is not thought to be as impor­tant as trash-borne inoculum. Importance Because the seed-borne phase is relatively unimportant compared with trash-borne inoculum the seed-borne phase does not often threaten yield. Net blotch is now a very important disease of barley and can cause large losses where the disease is not well controlled. The disease can be particularly damaging when Net blotch symptoms on barley

Splash dispersal of conidia up Strong air currents plant release conidia causing re-infection

Typical net-like symptons occur

At end of season pseudothecia develop Primary infection results from conidia and ascospores

Overwinters as seed-borne mycelium and as pseudothecia on crop debris Net blotch life cycle

56 Omphalina patch

Pathogen: Omphalina pyxidata

Wheat Barley Oats Rye Triticale

Hosts and then produces air-borne The disease affects wheat, barley basidiospores. These spores may and grasses. play a part in long distance spread of the disease. The role of basidiospores Symptoms is unclear. The disease is normally first seen as stunted areas of poor growth. Affected crops are frequently found on light land. Affected patches can be visible as early as December as sharply delineated but irregular areas of stunted growth although the crop remains a normal green colour. Roots and the soil adjacent to affected plants show characteris­tic white hyphal masses (like small pieces of cotton wool about 1mm across). Fruiting bodies (basidiocarps)­ like tiny mushrooms can sometimes be found within affected patches between January and March. They are approximately 2cm high with a 1cm diameter convex cap. Life cycle Little is known about the disease cycle although this is a soil-borne fungus which survives between sus­ceptible hosts as sclerotia or as mycelium on root debris. It infects crops soon after emergence, colonises roots, produces sclerotia Fruiting bodies in an infected patch of barley

57 Omphalina patch

Importance Until recently, the fungus had not been recognised as a pathogen of cereals in the UK. It is now believed to be sporadic in nature, affecting a small number of crops each year, mainly winter barley. Winter wheat is less frequently affected than barley­ and losses each year will be very small in comparison with other dis­eases. Limited trials on winter bar­ley suggest infection can reduce fer­tile tiller number by 40% and yields by 25–50%.

Close-up of the fruiting bodies (basidiocarps)

Basidiocarps seen in crop January to March Infected plants appear stunted and may develop white-heads

Long distance Healthy Diseased spread by air (stunted) borne spores

Overwinters as mycelium on crop debris and grass hosts White hyphal masses on roots (resemble small pieces of cotton wool)

Omphalina patch life cycle

58 Powdery mildew

Pathogen: Blumeria graminis f. sp. tritici – Wheat, Triticale; Blumeria graminis f. sp. hordei – Barley; Blumeria graminis f. sp. avenae – Oats; Blumeria graminis f. sp. secalis – Rye

Wheat Barley Oats Rye Triticale

Hosts All cereals can be affected by mildew although there are several forms of the disease which are spe­cific to individual crops and do not cross-infect. Symptoms Symptoms of powdery mildew can be found on leaves, stems and ears, but leaves are most commonly infected. Typically, white pustules appear which produce a mass of spores with a powdery appearance. As the mildew pustules become older, they darken to a grey or brown colour. Eventually, black spore cases (cleistothecia) can be found embedded in the mildew pus­tules – usually towards the end of the season. Life cycle Mildew overwinters primarily as mycelium on volunteers and autumn-sown crops. The cleistothecia pro­duced during late summer are resistant to low Mature mildew pustules with cleistothecia temperatures and drying which allows on wheat the fungus to survive in the absence of a host.

59 Powdery mildew

Typical white pustules on barley Early powdery mildew symptoms on wheat

In humid weather, cleistothecia germinate over a wide range of release the sexually produced temperatures, from 5–30°C, although ascospores which can initiate autumn 15°C is optimal with relative humidity infections.­ However, in the UK, green above 95%. Free water inhibits spore plant material is nearly always germination. Under dry con­ditions, available and cleistothecia are fresh spores can be formed in about thought to be of secondary seven days. At the end of the season, importance to mycelium. As volunteers and early autumn-sown temperatures rise in the spring, crops may become infected, dormant myceli­um starts to grow and providing inoculum for the following spores are quickly produced. These crop.

60 Powdery mildew

Importance Late-sown winter wheat crops are often particularly prone to attack, especially when growing rapidly in the spring. High levels of nitro­gen fertiliser encourage the disease and mildew can be particularly severe in dense crops. The visual appearance of the disease usually outweighs its damage potential especially during the autumn and winter. In susceptible varieties, yield losses can be high (up to 20%) and early control can be very important. However, the disease generally causes much smaller yield losses and late attacks (after flowering) on the flag-leaf and ear rarely cause significant losses.

Powdery mildew with cleistothecia on wheat

61 Powdery mildew

Young barley plant infected with powdery mildew

Re-infection of leaf layers by air-borne conidia

Mycelium develops on young plants conidiophores release conidia Cleistothecia develop on lower leaves

In spring, conidia and ascospores start early infections

Overwinters as mycelium and cleistothecia on crop debris, autumn-sown crops and volunteers Powdery mildew life cycle

62 Ramularia leaf spot

Pathogen: Ramularia collo-cygni

Wheat Barley Oats Rye Triticale

Hosts The disease affects only winter and spring barley. Symptoms Typical symptoms of ramularia comprise small brown rectangular lesions, often surrounded by a yellow halo. They resemble the spot-form of net blotch. Following high levels of infection, the leaves may senesce rapidly. Lesions are often obvious on dead leaves as black spots. The spores of the fun­gus are visible on the surface of dead leaves. Ramularia is frequently found in association with other leaf spots such as abiotic sun scorch, physiological leaf spot and spotting caused by damage to the leaf wax following the application of some fungicides. Life cycle Ramularia can be detected on the seed and within symptomless leaves. The disease can also be dispersed via air-borne spores. Symptoms can develop on dead lower leaves but symptoms are rarely seen on healthy green leaves until after flowering. Small, brown rectangular lesions of ramularia There may be a stress or physiological leaf spot trigger for symptoms to devel­op.

63 Ramularia leaf spot

The toxin rubellin D is also thought to be produced by the fun­gus when the barley host is stressed. Under certain light conditions, this toxin causes oxidative stress, lead­ing to plant cell damage and causing typical leaf symptoms. Importance Ramularia leaf spot can cause extensive damage to the upper leaves in spring and winter barley once crops have finished flowering. This can cause extensive losses in yield and quality. Yield losses in spring barley can be up to 0.6 tonnes per hectare.

Close-up of ramularia leaf spot lesions

Seedling infection Lesions on dead lower leaves Carried on seed Air-borne spores from cereal hosts Spread to upper leaves Conidia

Infection Under stress­ spreads to ear symptons on upper leaves

Ramularia leaf spot life cycle

64 Rhizoctonia stunt

Pathogen: Thanatephorus cucumeris (Rhizoctonia solani)

Wheat Barley Oats Rye Triticale

Hosts Life cycle The disease is known to affect all the The disease is soil-borne. The fun­gus major cereal crops and proba­bly is very common in soils and can most grasses. Barley is much more survive between susceptible crops as susceptible to the disease than other mycelium on dead tissues and other cereals. hosts. Symptoms Importance The disease is usually apparent as The disease is erratic in occurrence patches of thin stunted plants, which and frequently more severe where often show yellowing or pur­pling with crops have been established by die-back of seedlings in the autumn. direct drilling or minimum cultiva­tion. Patches may also become visible in Individual crops may suffer significant early spring as areas of stunted losses but in general wheat is not purpled plants. The root systems of seriously affected. Losses in barley plants within these patches are can be much more significant. usually poor and branched. Points of brown rotten tissue may be seen at intervals along the length of the root where they appear as constrictions, often giving the root the appearance of a string of sausages. Affected plants remain thin and stunted throughout the season and their maturity is often delayed. Affected crops are usually confined to sandy loam or loamy sands, in areas such as the Brecklands of Norfolk or Suffolk.

65 Rhizoctonia stunt

Roots of a stunted plant

Root infection weakens Affected plants often seedlings causing remain stunted patches of poor growth

In autumn and spring sclerotia germinate producing infectious hyphae

Overwinters in soil and on host debris as sclerotia and mycelium Rhizoctonia stunt life cycle

66 Rhynchosporium (leaf scald)

Pathogen: Rhynchosporium commune

Wheat Barley Oats Rye Triticale

Hosts The disease affects barley, rye, triti­cale and a number of grasses, par­ticularly ryegrasses. There are specialised­ forms of the pathogen which are generally restricted in their host range. Symptoms The fungus causes scald-like lesions on leaves, leaf sheaths and ears. Early symptoms are generally oval lesions which are pale green. As the lesions age they acquire a dark brown margin, the centre of the lesion remaining pale green or pale brown. Lesions often coalesce form­ing large areas around which leaf yellowing is very common. Infection often occurs in the leaf axil which can cause chlorosis and eventual death of the rest of the leaf. Life cycle The fungus is seed-borne but the importance of this phase of the disease is not fully understood. The most important source of the disease is probably crop debris from previous crops and volunteers which become Scald-like lesions showing dark brown infected from the stubble from margins and pale centres previous crops.

67 Rhynchosporium (leaf scald)

Autumn-sown crops can become infected very soon after sowing. The disease spreads mainly by rain­splash although long-distance spread by air-borne spores is also possible. Importance The disease can be very severe, particularly in the south west and west of the UK where conditions are generally mild and wet. The most serious effect on yield in both winter and spring barley results from attacks that develop between first node detectable and boot-swollen growth stages.

Rhynchosporium symptoms

Rain splash Infection causes causes blotch symptons spread of conidia up plant

Seedling infection Conidia from Seed infection fungal stromatic tissue is primary source of inoculum

Overwinters as mycelium in seed and on crop debris

Rhynchosporium (leaf scald) life cycle

68 Septoria tritici (septoria leaf blotch)

Pathogen: Zymoseptoria tritici (Mycosphaerella graminicola and Septoria tritici)

Wheat Barley Oats Rye Triticale

Hosts leaves. These contain the visible­ Mainly wheat, but also occasionally black pycnidia which are the most on rye, triticale and some grass characteristic feature of Z. tritici. species. Pycnidia are particular­ly common on dead over-wintering leaves of winter Symptoms wheat. Lesions on the mature plant are brown and are sometimes Symptoms of septoria can be seen restricted by veins giving a very early in the growing season in rectangular appearance. The black most years. On young autumn-sown pycnidia become more visible in the wheat, water-soaked patches which lesions as the symptoms develop. quickly turn brown and necrotic may Lesions may coalesce leading to be evident by early December and large areas of necrotic brown tissue. throughout the winter on the lowest

Brown, necrotic lesions on young wheat plant showing black pycnidia

69 Septoria tritici (septoria leaf blotch)

winter-sown crops are normally infect­ed by long distance spread of air-borne ascospores throughout the winter and early spring. In the spring the lower leaves of the most susceptible varieties are infected and have actively sporulating lesions. Most disease spread to upper leaves occurs by rain-splash from the lower-leaves during heavy rainfall. Physical spread can occur without Coalesced lesions giving large areas of heavy rainfall, particularly when necrotic brown tissue leaves 3 and 4 overlap the upper Life cycle leaves as they emerge. The disease cycle of Z. tritici. is Importance similar to that of S. nodorum, although Z. tritici. can go through This is the most important foliar its life cycle at slightly lower disease on winter wheat in the UK. temperatures with 15–20°C as the Losses of 50% have been reported in optimum and requires longer severely affected crops. This is periods of high humidity to initiate largely because of the predomi­nance infection. The lower leaves of of susceptible varieties.

Spread of pynidiospores up plants by contact and rain splash In autumn and spring, Pseudothecia and pycnidia crops infected by develop within lesions airborne ascospores

Perithecia Pycnidia (rain splash) (wind blown) Ascospores

Overwinters as mycelium, pycnidia and pseudothecia on crop debris, autumn sown crops and volunteers Septoria tritici (septoria leaf blotch) life cycle

70 Sharp eyespot

Pathogen: Ceratobasidium cereale (Rhizoctonia cerealis)

Wheat Barley Oats Rye Triticale

Hosts temperatures of around 9°C. Acid, The disease affects wheat, barley, dry and sandy soils and early sowing oats, rye and triticale. favour the disease. Symptoms Cool autumn or spring temperatures may result in early infection by the Symptoms occur as sharply defined fungus which can lead to severe lesions on the outer leaf sheaths. disease. Young lesions have a sharply defined dark margin and frequently have Importance shredding of the epidermis within the Sharp eyespot is common in the UK lesion. Multiple lesions up the stem although, nationally, it does not can be found up to 30cm from the usually cause significant yield loss. stem base. Later in the season, However, individual crops may suf­fer lesions on the stem have a pale significant losses, particularly if the cream centre with a dark brown, disease is present with take-all. sharply defined edge. Sharp eyespot Severe sharp eyespot has been lesions are often superficial, but shown to reduce yield by up to 25% severe sharp eye­spot is not but this is very unusual. Annual uncommon and can cause losses in the UK on average are white-heads or lodging. probably less than 0.5%. Life cycle The fungus over-winters primarily as mycelium on infected stubble with volunteers and some grass weeds also acting as sources of inoculum. The fungus can produce sclerotia which may act as over­wintering structures. Infection may occur at any time during the grow­ing season, but the disease is favoured by

71 Sharp eyespot

Distinct sharp eyespot lesions with sharply defined edge

Lesions can cause lodging and sometimes white-heads

Mycelial growth infects young plants Sharply defined lesions high up the stem

Overwinters on stubble, autumn-sown crops, volunteers, grass weeds and as a soil saprophyte

Sharp eyespot life cycle

72 Snow mould (pink snow mould)

Pathogen: Monographella nivalis (Microdochium nivale)

Wheat Barley Oats Rye Triticale

Hosts Life cycle Snow mould is mainly a disease of Winter-sown crops become infected winter barley, although other win­ter during the winter months, often under cereals are also occasionally affected. snow cover. The lower leaves of plants touching the soil surface Symptoms become infected by hyphae grow­ing Symptoms are typically seen after from perithecia or directly from plant snow melts in the spring. Infected debris in the soil. Affected plants or plants often have an extensive dead plant material carrying covering of white mycelium which perithecia or mycelial growth are spreads on overlapping leaves, returned to the soil after harvest. causing a matting of leaf tissue. Infected seed may also contribute to Later, as spores are produced on the initial infection of seedlings in the mycelial mats, the affected patches autumn. Spring sown crops are rarely assume a pink colouration. The affected. fungus often infects the oldest leaves directly from the soil but eventually Importance the whole plant can be affected. Snow mould is commonly recorded Plants die-off in patches, but good but, except in isolated cases, growing conditions in the spring can damage is rarely severe. The disease allow crop recovery where plants is generally more damaging in parts have survived infec­tion. In years with of Scotland where snow cover is prolonged snow cover, the disease more common. can be severe. Large areas of the crop may be killed and re-drilling with spring barley may then be necessary.

73 Snow mould (pink snow mould)

Damaged patch of young seedlings due to snow mould

Perithecia develop in late spring and summer Primary infections occur on lower leaves and stem base

Seedlings infected in autumn Conidia and mycelium by hyphae from perithecia, spread from debris ascospores and conidia

Overwinters on crop debris

Snow mould life cycle

74 Snow rot (grey or speckled snow mould)

Pathogen: Typhula incarnata

Wheat Barley Oats Rye Triticale

Hosts Life cycle Snow rot affects only winter cereals, Affected plants produce large especially winter barley, although numbers of sclerotia which can infections have been noted in winter survive between crops over-winter. wheat. The sclerotia germinate and produce spores and/or mycelium which infect Symptoms emerging crops. Winter-sown crops The fungus infects the oldest leaves become infected during the winter first but eventually the whole plant months, often under snow cover. can be affected causing yellowing Spring-sown crops are rarely and wilting. Affected plants usually affected. have abundant red-brown resting structures (sclerotia) 2–3mm in Importance diameter embedded in the lower leaf Snow rot is commonly recorded but, sheaths and on dead leaf tissue. except in isolated cases, damage­ is Plants can be killed, but often good rarely severe. The disease is generally growing conditions in the spring allow more damaging in parts of Scotland crop recovery. Surviving tillers where snow cover is more common. compensate for dead shoots so that yield loss is usually small. In years with prolonged snow cover, the disease can be more severe. Large areas of the crop may be killed and re-drilling with spring barley may then be necessary.

75 Snow rot (grey or speckled snow mould)

Resting structures (sclerotia) of snow rot on lower leaf sheaths

Sclerotia embedded in lower leaf tissue and roots Affected plants may be stunted Spores infect or killed growing crops Sclerotia outright produce fruiting bodies Overwinters as sclerotia in soil and on crop debris Mycelium spread from sclerotia to crops especially under snow

Snow rot life cycle

76 Sooty moulds

Pathogen: Alternaria spp. and Cladosporium spp.

Wheat Barley Oats Rye Triticale

Hosts Symptoms These fungi are saprophytes, are not The usual symptoms of sooty moulds host specific and so can affect all are a darkening of the ears before cereals. harvest. This is commonly seen when weather conditions are wet, but severe symptoms are often associated with root or stem base diseases which cause premature ripening of the crop. Delays in harvesting in wet weather can lead to severe blackening of ears which can lead to discolouration of the grain. Life cycle The fungi that can cause sooty moulds are very common in the Comparison of ears without and with sooty atmosphere and can survive adverse moulds conditions as spores or as mycelium on a wide range of materials. They do not require living host material to survive. Importance The discolouration of ears and grain rarely have any effect on grain yield but the mixing of spores with the grain at harvest can lead to discolouration which will affect marketability, particularly if the grain is planned for milling for flour production. Wheat ears severely affected by sooty moulds

77 Sooty moulds

Comparison of untreated and treated plots showing the difference in sooty mould infection

Colonisation of prematurely ripe ears or where aphid honeydew present Conidia infect ears post GS 75 White-heads often become severely affected by sooty moulds

Airborne conidia post GS 75

Alternaria

Cladosporium Overwinters on crop debris and vegetation

Sooty moulds life cycle

78 Stripe smut

Pathogen: Urocystis occulta

Wheat Barley Oats Rye Triticale

Hosts The disease is specific to rye. Symptoms This disease differs from the other smuts of UK cereals in that it affects not only the ears but also the stems and leaves. It is specific to rye, producing long dark blisters in stripes parallel to the veins which eventually rupture to expose the spores. Life cycle The disease is both soil-borne and seed-borne. The developing grains in ears are contaminated by wind-blown spores but the spores remain on the seed surface. Infection of the seed occurs at germination as with bunt. Soil-borne inoculum is more important with this disease than with the smuts affecting other cere­als in the UK. Importance The disease is sporadic in occur­rence Typical early symptoms of stripe smut but rarely causes significant loss.

79 Stripe smut

Sori develop between veins on Infected plants appear leaves and glumes yellowish and stunted

Fungus grows systemically within plant

In autumn and spring sporidia germinate. Sori erupt releasing spore Mycelium infects seedlings balls containing teliospores

germinating teliospore Overwinters as spore balls in soil and on seed Teliospores germinate forming promycelium and sporidia Spore balls

Stripe smut life cycle

80 Take-all

Pathogen: Gaeumannomyces graminis var. tritici Gaeumannomyces graminis var. avenae

Wheat Barley Oats Rye Triticale

Hosts Primary infection occurs in autumn Gaeumannomyces graminis var. tritici from inoculum in the soil. attacks wheat, barley, rye and may Secondary (root-to-root) infection attack some grass species, occurs mostly in spring and sum­mer. particularly couch grass (Elytrigia The disease spreads from infected repens).Oats are immune. seedling roots to develop­ing crown Gaeumannomyces graminis var. roots. As the disease pro­gresses, the avenae attacks oats, wheat, barley, root area lost increases and the ability rye and many grass species. of the plant to absorb water and nutrients declines. When root rotting Symptoms is severe plants are unable to absorb The take-all fungus attacks the roots water and nutrients. As a result the of plants as it is soil-borne. If plants ripen prematurely, resulting in diseased plants are pulled up, the white-heads and often poor grain roots can be seen to be blackened filling. and rot­ten and have a 'rat-tail' appearance. In severe outbreaks the Importance base of infected plants may also Take-all is one of the most impor­tant show black­ening. Above ground diseases of wheat in the UK, partly symptoms are seen as patches of because it is not easily con­trolled stunted plants and white-heads chemically or by varietal resistance ('bleached' ears) in mature plants. and relies mainly on rotational White-heads generally contain small strategies for control. Even on chalky grains or, occasionally, no grain at all. boulder clay soil, losses of 10–20% are common in second and third Life cycle wheat crops. On less well-bodied The take-all fungus survives the soils, yield losses can be much higher winter as mycelium primarily on roots or indeed it may be impossible to or stubble debris but also vol­unteer grow second or subsequent wheat. cereals, early autumn-sown crops Grain from plants showing and some grass weeds. white-heads are usually small and shrivelled.

81 Take-all

Take-all causes most damage on light soils, particularly if they are alkaline in nature. Severe attacks can also occur in acid patches. Poor drainage and nutrient status also encourage the disease. Take-all is particularly encouraged by early sowing and light, puffy seedbeds. The disease is usually most severe in second, third or fourth successive cereal crops, but generally declines in importance in continuous cereals (take-all decline).

Typical 'rat-tail' appearance of roots due to take-all

Severe infection results in stunted patches, 'rat tail' appearance and whiteheads

Runner hyphae White-head on roots

Fungus overwinters as mycelium on roots and stem bases of infected plants, Take-all life cycle spreading to volunteers and autumn-sown crops

82 Tan spot (DTR)

Pathogen: Pyrenophora tritici-repentis (Drechslera tritici-repentis)

Wheat Barley Oats Rye Triticale

Hosts Symptoms The disease affects wheat but can P. tritici-repentis can be seed-borne also attack barley, rye and some and infect seedlings, resulting in grasses. small tan to light brown flecks on young leaves. However, symptoms are generally seen later in the sea­son on the middle and upper canopy. Early symptoms appear as small tan to light brown flecks, with a chlorotic halo, often with a dark spot at the centre. Later these develop into light brown oval lesions with slightly darker margins with a light coloured spot at the centre. Under wet conditions the lesions produce spores which can make lesions darker in colour. Under ideal conditions these lesions coalesce to produce large areas of dead tissue. Life cycle P. tritici-repentis survives mainly as dormant mycelium on stubble and crop debris. This produces ­pseudothecia on stubble which in turn produce ascospores for long distance spread. Under warm, wet conditions, leaf spots produce dark conidia which are spread up the plant. The disease can infect the ear Spreading tan spot lesion with a chlorotic and cause discolouration of the halo and dark spot at the centre glumes and the grain.

83 Tan spot (DTR)

Symptoms on the head are indistinct but can cause brownish glumes. Infected grains can have a reddish appearance,­ similar to Fusarium spp. infection. The disease develops over a wide range of temperatures but has quite a high optimum (20–28°C) and is favoured by long peri­ods (18 hours or more) of dew or rain. Importance Tan spot is very common in Scandinavia and parts of France but is still rare in the UK. Although it is Tan spot symptoms occasionally recorded in dis­ease surveys it rarely causes serious losses. However, in a few isolated cases the disease has caused serious losses on individual crops grown under minimum tillage systems.

Rain splash moves conidia up plant Typical eye-shaped causing re-infection leaf spotting symptons occur

At end of season pseudothecia develop

Primary infection results from conidia and ascospores

Overwinters as seed-borne mycelium and as pseudothecia on crop debris

Tan spot (DTR) life cycle

84 Yellow (stripe) rust

Pathogen: Puccinia striiformis

Wheat Barley Oats Rye Triticale

Hosts Symptoms There are distinct forms of the fun­gus Yellow rust symptoms appear as that are specific to different cereal parallel rows of yellowish orange crops, ie P. striiformis f.sp. tritici coloured pustules on the leaves of attacks wheat whereas P. striiformis adult plants. Epidemics often start on f.sp. hordei can only attack barley. individual plants, usually in the Within the forms of P. striiformis there autumn. Symptoms develop slowly are a number of different races that over winter and are often missed until can only attack certain varieties. the early spring when small patches or foci of infected plants can be seen in fields. Early on, the yellow to orange coloured yellow rust pustules are difficult to distin­guish from brown rust. However, yellow rust lesions tend to spread as a yellow band on young leaves mov­ing ahead of the sporulating lesion. On older leaves pustules occur in obvious stripes hence it sometimes being referred to as stripe rust. Severe infections quickly give rise to chlorosis, and later necrosis, of leaves resulting in desiccation in May/June if the weather conditions are warm and dry. In severe attacks yellow rust infection of the ears can occur with the formation of masses of spores between the grain and the glumes. At the end of the season, secondary black spores (telio­spores) are sometimes produced amongst the Typical striped symptoms of yellow rust stripes of pustules.

85 Yellow (stripe) rust

Life cycle P. striiformis requires living green plant material in order to survive, over-wintering as dormant myceli­um or active sporulating lesions on volunteers or early autumn-sown crops. Within plant tissue the fungus­ can survive at very low temper­atures and will usually survive the winter in infected plants. In the spring, particularly in cool moist weather, the fungus starts to grow and produces active sporulating lesions. Temperatures of 10–15°C and a relative humidity of 100% are optimal for spore germination, penetration and production of new, wind- dispersed spores. The fungus is Yellow rust pustules on a wheat glume generally inhibited by temperatures­ Importance over 20°C although strains tolerant of The disease is generally sporadic in high temperatures do exist. The the UK occurring more often in the complete cycle from infection to the east of the country and in coastal production of new spores can take as areas which may have cool summer little as seven days with ideal weather accompanied by regular conditions and may be repeated mists. Severe epidemics are usually many times in one season. During associated with susceptible varieties,­ late summer, the dark teliospores mild winters and cool moist may be produced. These can summers. The development of new germinate to produce basidiospores, races of P. striiformis can result in however, no alter­nate host has been varietal resistance being overcome found. Although the teliospores seem within a short period of time. Yield to have no function in the disease losses of 40–50% have often been cycle they may contribute to the recorded in susceptible varieties. development of new races through sexual recom­bination.

86 Yellow (stripe) rust

Yellow rust focus Summer Disease spread by wind dispersal Pustules erupt releasing uredospores Late in the season black telia form on leaves

Autumn Early infection of plants by wind-borne uredospores Teliospores produce basidia Spring Overwinters and basidiospores on volunteer plants Alternate host (Berberis spp.) Yellow (stripe) rust life cycle

87 Glossary

Alternate host A second host (of a different plant species) required by some pathogens in order to complete their life cycle Anamorph The imperfect or asexual stage of a fungus Apothecium A cup- or saucer-like ascocarp Asexual Without sex organs or sex spores: vegetative Ascocarp A fruiting body which bears asci Ascospores Sexually produced spores contained within an ascus Ascus (pl. asci) A sac-like cell which contains the products of the sexual stage (teleomorph) as ascospores (generally 8) Basidiocarp A fruiting body which bears basidia Basidiospores (Sexually produced) spores borne on the outside of a basidium Basidium A cell or organ from which the sexually produced basidiospores (generally 4) are formed Biotroph An organism entirely dependent upon another living organism (the host) as a source of nutrients Break crop A crop (eg oilseed rape) grown in rotation with other crops (eg wheat) to improve the growing conditions of the following crop Chlamydospore An asexual spore arising from a hyphal segment, a resting stage Chlorosis The yellowing of normally green plant tissue Cleistothecia The closed spherical ascocarp of the powdery (chasmothecia) mildews Coleoptile Protective sheath surrounding the emerging shoot of a cereal Conidia Asexual fungal spores formed from the end of a conidiophore Conidiophore A specialised hypha on which one or more conidia are produced Cotyledon Part of the embryo that forms the primary leaf Crown roots The roots which emerge from the base of the stem of the plant rather than the seed

88 Glossary

Damping-off Disease of plant seedlings caused by seed- or soil-borne fungi Dicotyledon A flowering plant where the embryo has two cotyledons (seed leaves) Dieback Necrosis of a shoot beginning at the apex and spreading towards the older tissue, stem death may occur Direct drilling The drilling of seed into ground which has received minimal cultivation Ear blight Infection of cereal ears resulting in bleaching of parts of the ear or discolouration of the glumes and grains Endosperm Nutritive tissue in a seed Epidemic A widespread increase in the incidence of an infectious disease Epidermis The outermost layer of cells of an organ, usually only one cell thick Ergot The fruiting structure (sclerotium) of Claviceps spp. Flag leaf The final leaf to emerge in a cereal plant Focus A site of local concentration of diseased plants, usually about a primary source of infection or coinciding with an area originally favourable to disease establishment Forma specialis A group within a pathogen species that can only (f. sp) infect particular hosts Glume An outer and lowermost bract of a grass (including cereals) spikelet (inflorescence) Honeydew (fungal) A sticky secretion containing conidia produced during the lifecycle of Claviceps purpurea (Ergot) Host A living organism harbouring a pathogen Host specific Pertaining to a particular host, generally species specific Hypha One of the filaments of a mycelium

89 Glossary

Immune Cannot be infected by a given pathogen Inoculum Micro-organisms or virus particles which act as a source of infection Inflorescence The group or arrangement in which flowers are borne on a plant Internode Part of a plant stem between two successive nodes Leaf sheath The lower part of the leaf which surrounds the stem more or less completely Lesion A localised area of diseased tissue Lodging When a standing crop is caused to lean or bend due to adverse weather or soil conditions Minimal cultivation A reduced form of cultivation Morphology the form and structure of an organism Mosaic A pattern of disease symptoms on a plant apparent as green/yellow or dark/light areas, usually referring to virus infections Mycotoxin A toxin produced by a fungus Mycelium The mass of hyphae forming the body of a fungus Necrotroph Micro-organism feeding only on dead organic tissue Node The level of a stem at which one or more leaves arise Pathogen An organism which causes disease Perithecium An ascocarp shaped like a flask containing asci Primary inoculum Spores or fragments of mycelium capable of initiating disease Pseudothecia A peritheca-like structure with a single cavity containing ascospores Pustule A spore mass developing below the epidermis and then break­ing through at maturity Pycnidium Flask shaped fruiting body with an apical pore lined inter­nally with pycnidiospores Pycnidiospores Spores from within a pycnidium

90 Glossary

Rachis The main axis of the inflorescence, or spike, of wheat and other cereals, to which the spikelets are attached Resistance The inherent capacity of a host plant to prevent or reduce the development of a disease Saprophyte Nan organism deriving its nutrients from dead or decaying tissue of another organism Sclerotia Compact mass of fungal hyphae eg ergot, capable of being dormant for long periods, and giving rise to fruiting bodies or mycellium Seminal roots The roots developing directly from the seed Senescence The dying process of a plant or plant part Sporangiophore A hypha or fruiting structure bearing spores Sporangium A container or case of asexual spores. In some cases it functions as a single spore Spore A reproductive unit in fungi Sporulation The period of active spore production Susceptible A group within a pathogen species that can only infect particular hosts Telium Structure containing teliospores Teliospores Sexual spores produced within a telium Teleomorph The sexual or so-called perfect growth stage or phase in fungi Tolerance The ability of a plant host to sustain the effects of a disease without dying or suffering serious injury or crop loss Uredium The fruiting structure of a rust fungi in which uredospores are produced Uredospore The asexual spore of the rust fungus Vector An organism capable of transmitting inoculum Virulence The ability of a pathogen to produce disease White-head Prematurely ripened ears of cereals often caused by pathogens attacking the roots or stem base

91 Index

10 & 77 Alternaria spp. 36 Drechslera sorokiniana 6 Ascochyta leaf spot 55 Drechslera teres 6 Ascochyta spp. 83 Drechslera tritici-repentis 53 Barley mild mosaic virus 25 Dwarf bunt (BaMMV) 27 Ergot 8 Barley yellow dwarf virus 30 Eyespot (BYDV) 34 Flag smut 53 Barley yellow mosaic virus (BaYMV) 36 Foot rot 10 Black point 38 Fusarium ear/head blight 12 Black (stem) rust 38 Fusarium foot rot 59 Blumeria graminis f. sp. avenae 38 Fusarium seedling blight 59 Blumeria graminis f. sp. hordei 38 Fusarium spp. 59 Blumeria graminis f. sp. secalis 81 Gaeumannomyces graminis var. avenae 59 Blumeria graminis f. sp. tritici 81 Gaeumannomyces graminis 14 Brown (leaf) rust var. tritici 17 Bunt 44 Glume blotch 19 Cephalosporium gramineum 75 Grey snow mould 19 Cephalosporium leaf stripe 42 Halo spot 71 Ceratobasidium cereale 30 Helgardia acuformis 10 & 77 Cladosporium spp. 30 Helgardia herpotrichoides 27 Claviceps purpurea 19 Hymenella cerealis 36 Cochliobolus sativus 44 Leaf blotch 21 Covered smut 14 Leaf rust 23 Crown rust 67 Leaf scald 6 Didymella exitialis 47 Leaf spot 47 Drechslera avenae 49 Leaf stripe 49 Drechslera graminea

92 Index

51 Loose smut 63 Ramularia leaf spot 38 & 73 Microdochium nivale 71 Rhizoctonia cerealis 73 Monographella nivalis 65 Rhizoctonia solani 53 Mosaic viruses 65 Rhizoctonia stunt 69 Mycosphaerella graminicola 67 Rhynchosporium (leaf scald) 55 Net blotch 67 Rhynchosporium commune 53 Oat golden stripe virus (OGSV) 42 Selenophoma donacis 53 Oat mosaic virus (OMV) 69 Septoria leaf blotch 30 Oculimacula acuformis 44 Septoria nodorum 30 Oculimacula yallundae 44 Septoria seedling blight 57 Omphalina Patch 69 Septoria tritici 57 Omphalina pyxidata 71 Sharp eyespot 44 Phaeosphaeria nodorum 73 Snow mould 73 Pink snow mould 75 Snow rot 59 Powdery mildew 53 Soil-borne cereal mosaic virus (SBCMV) 23 Puccinia coronata 53 Soil-borne wheat mosaic virus 12 Puccinia graminis f. sp. tritici (SBWMV) 14 Puccinia hordei 77 Sooty moulds 14 Puccinia recondita 75 Speckled snow mould 14 Puccinia recondita f. sp. tritici. 55 Spot blotch 85 Puccinia striiformis 44 Stagonospora nodorum 14 Puccinia triticina 12 Stem rust 47 Pyrenophora avenae 17 Stinking smut 49 Pyrenophora graminea 79 Stripe smut 55 Pyrenophora teres f. maculata 81 Take-all 55 Pyrenophora teres f. teres 83 Tan spot (DTR) 83 Pyrenophora tritici-repentis 87 Stem rust 63 Ramularia collo-cygni

93 Index

65 Thanatephorus cucumeris 25 Tilletia controversa 17 Tilletia tritici 75 Typhula incarnata 34 Urocystis agropyri 79 Urocystis occulta 51 Ustilago avenae 21 Ustilago hordei 21 Ustilago kolleri 51 Ustilago nuda f. sp. hordei 51 Ustilago nuda f. sp. tritici 21 Ustilago segetum 51 Ustilago tritici 85 Yellow (stripe) rust 69 Zymoseptoria tritici

94 Further information

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